As is known, an object of the stereotaxic operation consists in exerting influence upon a specified cerebral structure, so-called "target structure", for the purpose of producing local destructions or stimulation in this structure. A stereotaxic instrument by means of which such influence is to be exerted can be introduced to the target structure from a number of different directions. However, for every structure there are certain preferred directions enabling to preclude the possibility of serious aggravations brought about by the traumatization of vitally important centers, large blood vessels, etc. by the stereotaxic instrument. Such preferred directions and their corresponding points of surgical access located on the skull of a patient are selected on the basis of the data on the brain anatomy.
In the prior art there is known a stereotaxic apparatus /cf. Japanese Patent No. 47-31591/ which comprises a base assembly f stened to the bone edges of a trepanation apperture, and two protractors arranged in perpendicular relation to each other, the first protractor being rigidly secured to the base assembly, while the second is pivotally mounted on said first protractor and is adapted to carry a guideway with a stereotaxic instrument. Subsequent to the fixation of the stereotaxic apparatus in the trepanation aperture contrast X-ray photographic procedures and stereotaxic calculations are performed to determine the direction and depth of penetration of the stereotaxic instrument insuring its accurate contact with the target structure, whereupon the stereotaxic instrument is positioned in conformity with the resultant calculated values by employing the scales of the protractors and the scale of linear displacements provided on the guideway of the stereotaxic instrument. In this case, since the base assembly is fastened with relation to the trepanation aperture there is only one direction of penetration of the stereotaxic instrument insuring its contact with the specified target point and, consequently, the only point of surgical access to the specified structure on the surface of the cerebrum. However, this point may be located within the area of a large blood vessel where even the slightest traumatization is inadmissible.
Thus, an apparent disadvantage of the described prior art stereotaxic apparatus lies in the impossibility of changing the point of surgical access in the trepanation aperture.
Improvement of the above stereotaxic apparatus is a stereotaxic apparatus disclosed in a paper by I. S. Vaskin "New modified apparatus and needle for stereotaxic operations on the brain", Proceedings of the joint neurosurgeons' Conference, Leningrad, 1964, pp. 141-142. Similarly, this stereotaxic apparatus has a base assembly fastened to the bone edges of a trepanation apetture and comprises two protractors arranged in perpendicular relation to each other and a guideway with a stereotaxic instrument associated therewith. However the structure in question differs from the aforesaid one in that the first protractor is mounted on the base assembly so as to be movable therealong. Hence, the use of such a stereotaxic apparatus admits of altering the point of surgical access, if desired, for instance, as in the case when the point of access is located within the area of a blood vessel. To accomplish this alteration the protractors are moved along the base assembly, and then another series of contrast X-ray photographic procedures and stereotaxic calculations are performed enabling to determine a new direction of penetration of the stereotaxic instrument and, consequently, a new point of surgical access to the given target structure.
However, inasmuch as the stereotaxic apparatus is fastened with relation to the edges of the trepanation aperture, all of the potential points of surgical access are naturally to be found within the confines of this particular trepanation aperture. Yet in a number of cases a patient may have been prescribed the introduction of a stereotaxic instrument into several target structures having their points of optimum surgical access located in different areas of the cerebral surface which are lying beyond the confines of the trepanation aperture. Thus, a disadvantage inherent in the stereotaxic apparatus under consideration consists in the impossibility of localizing the points of surgical access beyond the confines of that only trepanation aperture the bone edges of which have the base assembly of the stereotaxic apparatus fastened thereto.
Also known in the prior art is a stereotaxic apparatus /cf. U.S. Pat. No. 3,357,431/ comprising a crest frame adapted to be fixed to the cranium of a patient and having a carriage movably mounted thereon and provided with a vertical strut. The vertical strut is provided with a traverse secured thereto and having arms at each of its ends adapted to carry X-ray contrast sights. The traverse has a groove to receive a stereotaxic instrument disposed movably therein, with the stereotaxic instrument and the arms being arranged in one plane, and the X-ray contrast sights and the end of the stereotaxic instrument lying along one straight line being perpendicular to the mid-sagittal plane of the patient's brain.
The spatial position of the target point relative to the stereotaxic apparatus is determined by means of contrast X-ray photography performed in two mutually perpendicular projections, and stereotaxic calculations. The carriage is moved along the plane paralled to the mid-sagittal plane of the cerebrum so as to adjust on a profile X-ray picture the projections of the X-ray contrast sights to the projection of the target point, and then the stereotaxic instrument is moved along the traverse in a straight line perpendicular to the mid-sagittal plane of the cerebrum so as to adjust on a frontal X-ray picture the projection of the stereotaxic instrument to the projection of the plane parallel to the mid-sagittal plane of the cerebrum and extending across the projection of the target point, whereafter the stereotaxic instrument is introduced into the trepanation aperture.
The stereotaxic apparatus described hereinabove furnishes surgical access to various target structures through the points on the cerebral surface which are not to be necesserily located within the confines of one trepanation aperture, but may be sufficiently spaced apart. However when employing the foregoing stereotaxic apparatus the scope of surgical access to the target structures is yet limited since with the introduction of the stereotaxic instrument into the target structure the instrument is capable of moving exclusively along the plane parallel to the mid-sagittal plane of the cerebrum. Hence, if the above stereotaxic apparatus is to be used for the purpose of stereotaxic exposure applied to the cerebral structures located in the proximity of the mid-sagittal plane, then the points of surgical access to these structures will be localized adjacent to the sagittal sinus, which is highly perilous to the patient.
Another stereotaxic apparatus known in the prior art /see T. Riechert's paper "Die stereotaktischen Hirnoperation", Deutsche Medischen Wissenschrift, 1959, vol. 84, pp. 1669-1683/ comprises a base ring with head clamps, a half-ring plate coupled to the base ring and having a carriage movably mounted thereon and adapted to hold a stereotaxic instrument. The plate has its ends attached to bushings mounted on two bars so as to be rotable thereabout. The bars are secured to the base ring in a rigidly fixed position and can be detached therefrom allowing the removal of the plate with the stereotaxic instrument from the base ring.
This stereotaxic apparatus is utilized in combination with a stereotaxic apparatus model representing an exact replica of the base ring, with a point adapted to simulate the intracerebral space target point being set forth in the stereotaxic apparatus model and its position relative to the stereotaxic apparatus being determined by means of contrast X-ray photographic procedures conducted in two mutually perpendicular, projections, and stereotaxic calculations. The adjustment of the stereotaxic instrument to the target point is effected in the following manner.
The plate with the stereotaxic instrument is mounted on the stereotaxic apparatus model fixing the bars at the locations corresponding to those at which they were secured to the base ring of the apparatus. By rotating the bushings about the bars and moving the carriage relative to the plate the stereotaxic instrument is adjusted to the point of the stereotaxic apparatus model included therein to simulate the target point, with the direction of penetration of the stereotaxic instrument being chosen in accordance with the localization of the preselected point of surgical access. Subsequently, the position of the carriage on the plate and the position of the bushings relative to the bars are fixed, the bars are detached from the stereotaxic apparatus model, the plate with the stereotaxic instrument is mounted on the base ring of the stereotaxic apparatus fastened by means of the clamps on the patient's head, and the stereotaxic instrument is introduced into the target structure through a trepanation aperture.
While using the above stereotaxic apparatus, the points of surgical access may be located both in any region of the trepanation aperture and in different trepanation apertures as well, the direction of penetration that the stereotaxic instrument is at that not limited by any planes whatsoever, in particular, by the planes parallel to the mid-sagittal plane of the cerebrum. However in those cases where prior to the introduction of the stereotaxic instrument into the target structure there arises the necessity of changing the point of surgical access, for example, due to the inaccurate performance of a trepanation aperture when one of the bone edges of the aperture prevents the stereotaxic instrument from free movement, or due to the detection of a blood vessel previously left unnoticed in the area of the point of access, the aforedescribed procedures are to be carried out once again. In doing so, the plate with the stereotaxic instrument is transferred from the base ring of the stereotaxic apparatus onto the stereotaxic apparatus model, by rotating the bushings about the bars and moving the carriage along the plate, the stereotaxic instrument is adjusted to the point of the stereotaxic apparatus model, included therein to stimulate the target point, through a new point, and a new position of the carriage and the bushings is fixed. Subsequently, the plate with the stereotaxic instrument is removed from the stereotaxic apparatus model and mounted on the base ring of the stereotaxic apparatus fastened on the patient's head. The necessity of repeating these procedures substantially increases the duration of neurosurgical intervention and the level of traumatization.
The abovementioned disadvantages are obviated in a stereotaxic apparatus /see L. Laitinen's paper "A new stereoencephalotome", Zentrenblatten Neurochirurgie, 1971, vo.. 32, H.1-2, pp. 67-68/ comprising a ring provided with head clamps and incorporating a half-ring plate mounted thereon and adapted to support a carriage with a stereotaxic instrument, with the latter being disposed radially relative to the plate. The plate has its ends rigidly attached to two bushings mounted on two hollow bars so as to be rotable thereabout and movable therealong. The bars are movably joined to the ring and can be shifted in two mutually perpendicular directions i.e. along the plane of the ring and perpendicular to this plane.
In compliance with the requirements of the X-ray photography and stereotaxic calculations the above stereotaxic apparatus is placed on the head of a patient so that the axes of the hollow bars are perpendicular to the mid-sagittal plane of the patient's brain. The position of the target point with respect to the sterotaxic apparatus is determined by means of X-ray photographic procedures and stereotaxic calculations. By shifting the bars with respect to the ring, and the bushings along the length of the bars, the half-ring periphery center of the plate is adjusted to the target point, and the positions of the bars on the ring and of the bushings on the bars resulting from such adjustment are fixed, whereupon the plate can be rotated about the bars, and the stereotaxic instrument can be moved along the plate. If the length of the stereotaxic instrument is equal to the radius of the half-ring of the plate, then the end of the stereotaxic instrument with any position of the carriage on the plate and of the plate relative to the ring will be brought into coincidence with the half-ring periphery center of the plate and, consequently, with the target point.
Thus, the foregoing stereotaxic apparatus provides the possibility of gaining surgical access to some certain target struczure through a plurality of points on the cerebral surface, while the direction of introduction of the stereotaxic instrument into the target structure is not limited by any planes whatsoever. Furthermore, in order to alter the point of surgical access there is no need for performing any additional contrast X-ray procedures, or stereotaxic calculations, or manipulations involving the transference of the plate with the stereotaxic instrument onto the stereotaxic apparatus model, since in order to accomplish this alteration it is sufficient to merely turn the bushings about the bars and/or to move the carriage with the stereotaxic instrument along the plate.
Still the stereotaxic apparatus as described above has significant disadvantages which consist in the following. The hollow bars having the bushings mounted thereon and attached to the plate are capable of moving relative to the ring only progressively in two mutually perpendicular directions. Hence, for every target point there is only one position of the bars relative to the ring insuring accurate contact of the sterotaxic instrument with this target point. The target point in this position is to be located in the straight line which is an extension of the axes of both of the hollow bars. The bars impose limitations on the movement of the carriage with the stereotaxic instrument along the plate. Due to this fact for every target structure there are two zones whence surgical access is unfeasible. Practically, when employing the above stereotaxic apparatus such limitations apply to a large area of the temporal regions wherein are located the points of access providing the shortest paths to the structures of the temporal lobes.
Moreover, turning of the plate about the bars will always be restricted in the actual conditions of the stereotaxic operation due to such hindrances as a head-rest, an operating table, the trunk of a patient, etc.
Thus, a disadcantage of this prior art stereotaxic apparatus lies in the presence of the regions on the surface of the skull where surgical access to the target point is unattainable.
Further, with penetration of the stereotaxic instrument into the brain the plate made in the form of a half-ring, is positioned over the trepanation aperture and blocks the operating field interfering with the surgeon. Therefore, another disadvantage of the aforedescribed stereotaxic apparatus lies in that while using it access to the operating field is limited.